In manufacturing semiconductor elements, lithographic techniques have been employed in which a photoresist coating is formed on a substrate such as a silicon wafer, then selectively irradiated with actinic rays, and subjected to development processing to thereby form a resist pattern on the substrate.
In recent years, in order to attain much higher degree of integration in LSI, a patterning technique to form a pattern with a finer line width by a lithographic process has made a rapid progress. For forming a pattern with a finer line width, various proposals have been made with respect to all steps of the lithographic process and all materials to be used therein including photoresists, antireflective coatings, exposing methods, exposing apparatus, developing agents, developing processes and developing apparatus. For example, Japanese Patent No. 2,643,056 and Japanese Unexamined Patent Publication (JP-A) No. H7-181685 describe that a surface antireflective coating containing a fluorine-containing compound with a low refractive index is formed on a resist layer to thereby prevent detrimental influences of reflected light from the resist surface on formation of a resist pattern. To form an antireflective coating on a resist layer provides the advantage that, since degree of vibration amplitude of the thickness of a resist layer vs. sensitivity curve becomes smaller, the fluctuation in sensitivity of the resist layer becomes smaller even when the thickness of the resist layer fluctuates, which leads to a decreased fluctuation in dimension of resist patterns formed. In addition, the surface antireflective coating serves to decrease standing waves caused by interference between incident light and reflected light or between one reflected light and another reflected light. Recently, techniques of forming a resist pattern having a desired line width without providing the surface antireflective coating have also been developed. For example, an underlying substrate is made plane to depress fluctuation in dimension of a resist pattern due to fluctuation in thickness of the-resist layer as described above, or a mask pattern is finely adjusted beforehand according to fluctuation in dimension of the resist pattern.
With regard to exposing apparatus, there has been proposed a process of using a light source emitting radiation of a short wavelength, which is advantageous for forming a finer pattern, such as deep UV rays of KrF excimer laser (248 nm) or ArF excimer laser (193 nm) or, further, X rays or electron beams, and some of them have been coming into practice.
On the other hand, improvement in the yield of semiconductor integrated circuits has occupied the attention as an extremely important matter in manufacturing them. There exist many factors that deteriorates the yield of semiconductor integrated circuits. One of the factors is patterning failure upon forming a pattern using a resist. This patterning failure of a resist pattern is caused, for example, by dust existing in the resist or on the surface thereof, by deterioration of the resist due to basic species floating in a clean room, by coating failure of the resist, by development failure or the like. As an example of deterioration of resist due to chemical species floating in a clean room, there is illustrated deterioration of resist in a process using a chemically amplified photoresist. In this process, the chemically amplified photoresist is so susceptible to the influence of basic substances and moisture in the atmosphere that there results a change in dimension of a pattern—for example, a T-topped resist pattern results when a positive-working photoresist is used, or a round-topped resist pattern results when a negative-working photoresist is used—in case when the period between patternwise exposure and PEB (post exposure bake) is prolonged or due to intermixing with a resist.
To solve these problems described above, radiation sensitive resin compositions have been examined and their environmental resistance has been improved. From the viewpoint of the constitution of the radiation sensitive resin composition, there has been proposed improvement of the environmental resistance of the composition by incorporating basic sulfonium or basic ammonium compounds (JP-A H6-242605, JP-A H6-242605 and JP-A H6-242606), or by lowering the glass transition point of the resin thereby reducing the free volume of the resin, thus decreasing the amount of basic materials adsorbed into the radiation-sensitive resin composition (J. Photopoly. Sci. Tech. vol. 6, No. 4, pp. 547–562, 1993). In addition, there has been proposed further improvement of the environmental resistance of the composition by further specifying the resin (JP-A H9-80753). Further, use of organic materials such as polyethylene and an acidic polymer (JP-A H7-295228) or paraffin film (JP-A H11-95442) as a protective film on the radiation-sensitive resin composition has also been proposed. Even by these techniques, however, the problems described above are not completely solved under the present situation with regard to chemically amplified photoresists such as ones being sensitive to ArF laser light source having an exposure light wavelength of 193 nm.
Under these circumstances, an object of the present invention is to provide a method capable of forming resist patterns having good shape by reducing the influence of floating basic species on chemically amplified photoresists, as well as a treating agent used in the method.